Dr Eufemiano Fuentes is currently on trial in Madrid. Photograph: Action Press/Rex Features

An unknown number of cyclists, athletes and footballers face having their doping histories revealed after the doctor at the heart of a major drugs-in-sport network, Operación Puerto, suggested he may finally name names. Dr Eufemiano Fuentes, who is on trial in Madrid, told journalists outside the court on Wednesday that he would consider revealing his list of clients to the World Anti-Doping Agency (Wada).

"If they think that I can be useful to them and they ask me, I would consider it and would be available," Spain's state-owned EFE news agency reported. "What I don't know is whether what I can give them would be of any use."

Fuentes made his ambiguous offer as the trial, which has seen cyclists such as Tyler Hamilton, Ivan Basso and Jörg Jaksche give evidence, entered its final stages.

Fuentes denied he was trying to plea-bargain with anti-doping authorities who have hired lawyers to help prosecute him. "This would be in exchange for mutual collaboration," he said. "If the list was necessary within this collaboration, they would get it."

He is one of five people on trial who face prison charges of up to two and half years on public health charges.

Prosecutors are unable to charge him with breaking anti-doping laws, because these were not in place in Spain when his Madrid laboratory was raided in 2006 during a police operation known as Operación Puerto.

Evidence has revolved around 216 bags of plasma and blood found in fridges and freezers, most of which were marked with codenames. Wada has said it wants the bags so that it can do DNA tests to find the owners, but the court had declined to hand them over.

The bags were allegedly used for re-transfusions by cyclists and others who wanted to increase their red blood cell count.

Although Hamilton and others admitted that they had used Fuentes's services, mystery surrounds the real identities of dozens of other sports people who were clients.

They allegedly include many more cyclists, as well as Spanish Olympic athletes and professional footballers from Brazil and Spain.

Basso told the court he used his dog's name, Birillo, to mark his blood bags but many other codenames remain unsolved.